What is wavefront?

Since 1862, when Dutch ophthalmologist Herman Snellen first designed a standard test for visual acuity, we’ve used the Snellen Chart as a basis for testing our vision.

His familiar black and white chart of ever smaller letters first introduced the idea of ‘standard vision’, and enabled eyecare professionals to determine where a person sits in comparison with the rest of the population.

Suddenly by standing 20 feet away from a chart and reading through lines of letters, one could discover where they are on a universal spectrum of vision. And as a result could find out if they have a refractive error, such as myopia or hyperopia, and to what degree.

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Today, most eyecare professionals use an updated version of Snellen’s invention known as the logMAR chart along with other advanced testing equipment. But the fundamentals by which we assess vision has largely stayed the same for the past 150 years.

This is a problem as we’re only able to treat our eyes according to the data we have about them. Our eyes are much more complex and unique than a generic glasses prescription; it’s just that for a long time this has been the limit of our knowledge and technology.

In reality, on top of common refractive errors, there’s actually a small percentage (around 5 to 10 percent) of our vision that cannot be corrected by glasses.

This means two people who have the same glasses prescription don’t necessarily see the same. One may see sharper details than the other because they have fewer ‘higher order aberrations’. Whereas refractive errors like short-sightedness, long-sightedness, and astigmatism are known as lower-order aberrations and affect entire fields of vision, those of a higher-order only affect the finer aspects of vision. How well you see depends not just on one or the other but both.

The method of mapping these higher-order aberrations is known as wavefront analysis. These tiny irregularities, that can occur anywhere within the eye’s optical system, affect things like contrast sensitivity and sharpness and are measured using a wavefront aberrometer. In essence, the lower order aberrations represent visual quantity and higher order aberrations represent visual quality.”

A wavefront aberrometer works by measuring the light passing through your eye’s optical system (the lens and cornea). A map of the imperfections in your eye is produced by comparing the light detected by the device against a perfectly flat baseline.

These higher-order aberrations are too complex to be included within a glasses lens prescription – the lens sits too far from the eye, so it is not possible to align the irregular lens with the eye. Wavefront error can be included in special contact lenses, but these are more expensive, and usually reserved for patients with distorted corneas, such as a patient with keratoconus. However, the data from wavefront analysis can be fed into the laser for a more accurate laser eye surgery treatment plan and more precise results. Having said that, the level of higher order aberrations is very low for most patients, so the more important factor for laser eye surgery is in controlling the change in higher-order aberrations by the treatment, as increasing these too much can lead to visual symptoms such as halos, glare and starbursts.

Most good clinics include wavefront analysis in their treatments. However, if you want to ensure you achieve your best possible vision, you also need to be wary of spot size.

Wavefront aberrometers vary in their effectiveness according to the number of spots they use to map the cornea. This can be as low as 60 to as high as 902.The Zeiss WASCA in use at London Vision Clinic has a resolution of 650.

The difference between a low and a high-resolution analyser is like the difference between a watercolour and a high definition photograph. Whereas the watercolour gives a vague and indistinct impression of a landscape, the HD photo replicates it in all its finest detail.

Prof Reinstein answers the question “What is Wavefront?” and describes how a treatment that includes wavefront differs from one that only treats a glasses prescription.

Simply put, wavefront can give you that little bit more focusing power that glasses and conventional Laser Eye Surgery alone cannot achieve. But the exact outcome can depend on what aberrometer a clinic uses. For best results, find a clinic that includes wavefront analysis as standard and uses only the latest technology.

If you’d like to find out more about wavefront or book a consultation with us, leave us a comment or call us on 020 7224 1005.